1. Field of the Invention
The present invention generally relates to medical devices and methods of use for the treatment and/or management of cardiovascular, renal, and neurological disorders. Specifically, the present invention relates to devices and methods for controlling the low-pressure baroreflex system for the treatment and/or management of cardiovascular, renal, and neurological disorders.
Cardiovascular disease is a major contributor to patient illness and mortality. It also is a primary driver of health care expenditure, costing more than $326 billion each year in the United States. Hypertension, or high blood pressure, is a major cardiovascular disorder that is estimated to affect over 50 million people in the United Sates alone. Hypertension occurs when the body's smaller blood vessels (arterioles) constrict, causing an increase in blood pressure. Because the blood vessels constrict, the heart must work harder to maintain blood flow at the higher pressures. Although the body may tolerate short periods of increased blood pressure, sustained hypertension may eventually result in damage to multiple body organs, including the kidneys, brain, eyes and other tissues, causing a variety of maladies associated therewith.
Heart failure is the final common expression of a variety of cardiovascular disorders, including ischemic heart disease. It is characterized by an inability of the heart to pump enough blood to meet the body's needs and results in fatigue, reduced exercise capacity and poor survival. It is estimated that approximately 5,000,000 people in the United States suffer from heart failure, directly leading to 39,000 deaths per year and contributing to another 225,000 deaths per year. Heart failure results in the activation of a number of body systems to compensate for the heart's inability to pump sufficient blood. Many of these responses are mediated by an increase in the level of activation of the sympathetic nervous system, as well as by activation of multiple other neurohormonal responses. Generally speaking, this sympathetic nervous system activation signals the heart to increase heart rate and force of contraction to increase the cardiac output; it signals the kidneys to expand the blood volume by retaining sodium and water; and it signals the arterioles to constrict to elevate the blood pressure. The cardiac, renal and vascular responses increase the workload of the heart, further accelerating myocardial damage and exacerbating the heart failure state. Accordingly, it is desirable to reduce the level of sympathetic nervous system activation in order to stop or at least minimize this vicious cycle and thereby treat or manage the heart failure.
A number of drug treatments have been proposed for the management of hypertension, heart failure and other cardiovascular disorders. These include vasodilators to reduce the blood pressure and ease the workload of the heart, diuretics to reduce fluid overload, inhibitors and blocking agents of the body's neurohormonal responses, and other medicaments. Various surgical procedures have also been proposed for these maladies. For example, heart transplantation has been proposed for patients who suffer from severe, refractory heart failure. Alternatively, an implantable medical device such as a ventricular assist device (VAD) may be implanted in the chest to increase the pumping action of the heart. Alternatively, an intra-aortic balloon pump (IABP) may be used for maintaining heart function for short periods of time, but typically no longer than one month. Other surgical procedures are available as well. No one drug, surgical procedure, or assist system, however, has provided a complete solution to the problems of hypertension and heart failure.
For these reasons, it would be desirable to provide alternative and improved methods for treating hypertension, heart failure, and other cardiovascular, neurological, and renal disorders. Such methods and systems should allow for treatment of patients where other therapies have failed or are unavailable, such as heart transplantation. It would be further desirable if the methods could lessen or eliminate the need for chronic drug use in at least some patients. Additionally, it would be desirable if the methods and systems were mechanically simple and inherently reliable, in contrast to complex mechanical systems such as VAD's, IABP's, and the like.
One particularly promising approach for improving the treatment of hypertension, heart failure, and other cardiovascular and renal disorders is described in published PCT Application No. WO 02/026314, which claims the benefit of U.S. patent application Ser. No. 09/671,850, which is the parent of the present application. The full disclosures of both WO 02/026314 and U.S. Ser. No. 09/671,850, are incorporated herein by reference. WO 02/026314 describes the direct activation of baroreceptors for inducing changes in a patient's baroreflex system to control blood pressure and other patient functions. The prior applications are particularly directed at the activation of the baroreceptors present in the carotid sinus and the aortic arch. Both the carotid sinus and aortic arch are on the high-pressure or arterial side of the patient's vasculature. They are referred to as high-pressure since pressures in the systemic arterial circulation are higher than those in the veins and pulmonary circulation. Activation of the high-pressure baroreceptors can send signals to the brain that cause reflex alterations in nervous system function which result in changes in activity of target organs, including the heart, vasculature, kidneys, and the like, typically to maintain homeostasis.
While highly promising, the need to implant electrodes or other effectors on the arterial or high-pressure side of the vasculature may be disadvantageous in some respects. Arteries and other vessels on the high-pressure side of the vasculature are at risk of damage, and implantation of an electrode on or in the carotid sinus or aortic arch requires more care, and improper device implantation on the arterial side presents a small risk of arterial thromboembolism which in turn can cause stroke and other organ damage. Some arterial locations can also cause unwanted tissue or nerve stimulation due to current leakage.
Thus, it would be desirable to provide improved methods and systems for artificial and selective activation of a patient's baroreflex system in order to achieve a variety of therapeutic objectives, including the control of hypertension, renal function, heart failure, and the treatment of other cardiovascular. and neurological disorders. It would be particularly desirable if such methods and systems did not require intervention on the arterial or high-pressure side of a patient's vasculature, thus lessening the risk to the patient of arterial damage and damage resulting from thromboembolism or hemorrhage. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
U.S. Pat. Nos. 6,073,048 and 6,178,349, each having a common invention with the present application, describe the stimulation of nerves to regulate the heart, vasculature, and other body systems. Nerve stimulation for other purposes is described in, for example, U.S. Pat. Nos. 6,292,695 B1 and 5,700,282. Publications describing baropacing of the carotid arteries for controlling hypertension include Neufeld et al. (1965) Israel J. Med. Sci 1:630-632; Bilgutay et al., Proc. Baroreceptors and Hypertension, Dayton, Ohio, Nov. 16-17, 1965, pp 425-437; Bilgutary and Lillehei (1966) Am. J. Cariol. 17:663-667; and Itoh (1972) Jap. Heart J. 13: 136-149. Publications which describe the existence of baroreceptors and/or related receptors in the venous vasculature and atria include Goldberger et al. (1999) J. Neuro. Meth. 91:109-114; Kostreva and Pontus (1993) Am. J. Physiol. 265:G15-G20; Coleridge et al. (1973) Circ. Res. 23:87-97; Mifflin and Kunze (1982) Circ. Res. 51:241-249; and Schaurte et al. (2000) J. Cardiovasc Electrophysiol. 11:64-69.